Ozone is an allotropic form of oxygen, which is produced in nature by the exposure of oxygen molecules (O2) to ultraviolet light or to the high voltage associated with lightning. Such exposure breaks apart the oxygen molecules into mono-atomic oxygen and recombines a portion of the oxygen atoms and molecules to form ozone (O3). Manmade ozone is created by the passage of dry, ambient air or pure oxygen either past a source of ultraviolet light or through an electrical discharge, commonly called a corona, which is produced by an electric charge between parallel or concentric electrodes separated by a dielectric to prevent a spark discharge. Ozone produced by corona discharge typically is of a higher concentration than ozone produced by ultraviolet light, thus is rendered more useful for oxidation and purification applications such as may be employed for treatment of liquids and surfaces, as well as odor removal for indoor air. The formation of ozone via the corona discharge method has a concurrent formation of nitrous compounds, which, in the presence of moist air, precipitate small amounts of nitric acid inside the ozone generation chambers. Therefore, air dryers producing very low dew point air are typically employed along with the ozone generator to prevent the acid precipitation from fouling dielectrics and reducing ozone production capabilities.
Ozone is recognized as a potent sanitizer for rinsing and treating foods and surfaces in both aqueous and gas phase. It also is a proven water purifier as well. Ozone is a highly reactive oxidizer, the application of which as a sterilizing and preserving agent is well known. It is the most powerful disinfectant commonly available for food sanitizing and for water treatment and is capable of destroying bacteria up to 3,125 times faster than chlorine. Its ability to destroy such bacteria as E. Coli virtually on contact is well documented as is its effectiveness against such germs as staphylococcus and salmonella. In 1997 the United States Food and Drug Administration recognized and approved ozone as a process for sanitizing the surfaces of food. The bottled water industry, together with the US Food and Drug Administration and many state health agencies, which regulate bottled water production, recognize the purification and post-sanitizing efficiency of ozone and specify that an ozone residual in bottled water shall be between 0.1 and 0.4 Parts Per Million. Ozone's ability to minimize microbiological contamination on the surfaces of meat, cheese, eggs, poultry, fruits, vegetables and so forth has been known since the early 20th century. The treatment of foodstuffs with ozone has been successfully applied both in aqueous phase and gas phase. The resulting enhancement to food safety and the extension of shelf life of such items has made ozone a valuable adjunct to modern food processing and storage operations.
More recently, in studies by the Clemson University Department of Dairy Science, ozone has been proven to be a powerful sterilizer and sanitizer of microbiologically contaminated surfaces that have been subjected to a stream of ozonated water. Further recent studies by the Food Science and Nutrition Department of California Polytechnic University, San Luis Obispo, in conjunction with the inventor of the present invention, confirmed that common microbiological contaminants on food surfaces such as total coliforms, e. coli, e. coli 0157:H7, salmonella, listeria, campylobacter, shigella and staphylococcus can be significantly reduced by low level dissolved ozone application ranging from 0.1 to 0.3 Parts Per Million (PPM). Unlike chemical sanitizers, ozone leaves no chemical residue on treated surfaces, thus it is a highly desirable technology for use in large food processing plants as well as in small commercial applications, such as restaurants, and in personal household use for rinsing such items as dishes, cutting boards, utensils, kitchen sponges, meat trays and so forth, as well as foods. While large-scale ozone food sanitizing process systems have become common, there has been no viable ozone-based sanitizing device available for household or small commercial process applications. As the public becomes more aware of the importance of controlling microbiological contamination of food and surfaces, as well as of water, an effective means of applying ozone purification and sanitization that is simple, safe and economical is needed.
Ozone is indiscriminate in its reaction with microbes, therefore a device for applying such low level ozone amounts for aqueous phase food sanitizing must include a means of assurance that the water into which the ozone is injected is microbiologically pure so that there is little or no ozone demand present to reduce the ozone available for sanitizing rinse. Additionally, the ozone must be applied in a manner that thoroughly and reliably dissolves the low level ozone at a range of water pressure and flow rates that may be encountered in the field. The ozone injector would ideally incorporate a reliable means for protecting the ozone generator from water backing up into the generation electrodes. Additionally, the application of gaseous phase ozone for odor control in ambient air, as well as on selected items, would be a desirable feature as an optional use for such a generation device.
An ozone generator for such application as described needs to be simple, economical and convenient to use. Additionally, it needs to produce relatively high concentration of ozone from ambient air capable of maintaining dissolved ozone residuals in a range of 0.1 to 0.4 PPM. Preferably, such a generator would be of simple construction, which requires minimal service and maintenance. A desirable feature of a simple ozone generator would be its capability to function at full capacity without the necessity of drying the air feed to the ozone generation electrodes. Although there have been attempts to create cleanable electrodes, the inevitable buildup of nitric acid combined with ambient dust and similar contaminants in electrode components that are inaccessible makes the long term operation of such devices problematic. A related problem is that the ultimate buildup of dusty, sticky, acidic film which is difficult to remove may increase the dielectric strength of the dielectric over time, reducing the power of the corona, which results in the reduced concentration of ozone produced.
One of the greatest drawbacks of small under-the-counter or countertop ozone systems has been the use of air dryers to prevent the build up of nitric acid on ozone generator dielectrics. Small air dryers for such applications typically have consisted of containers of silica gel, molecular sieve or similar moisture absorbing agents. These agents must be regenerated frequently via the application of high heat. This regeneration necessity contributes to an excessive maintenance task, which is impractical for the average household or small commercial operation. Although automatically regenerating air dryers are available, they are generally too expensive to make such a system practical from a marketing point of view.
Another drawback for previously designed systems has been the method of dissolving ozone in the water. The two primary methods employed have been bubbling or sparging ozone into a container of water or using a venturi injector to draw the ozone into a stream of water. The first of these two methods creates limitations as to the amount of water that can be treated during a given time period since it relies on the complete direct contact of virtually every molecule of water with ozone molecules. This time factor precludes bubbling as a practical method for purifying a continuous stream of water although the technique remains viable when directed to a small container of water. The second method cited, venturi injection, can be highly efficient, but previous attempts to apply ozone have not addressed efficient injection design across a range of pressure and flow rate conditions. The technology requires a very specific pressure differential across the venturi in order for, first the ozone to be drawn into the water and, second, for the ozone to be thoroughly and violently dissolved in the water for maximum microbiological and oxidative effect. The general function parameters of a venturi-based ozone injection system require carefully controlled pressure factors both upstream and down stream of the injector.
A major limitation of venturi-based ozone systems has been the lack of a downstream faucet or dispenser valve that maintains adequate free flow without creating a backpressure that defeats the ability of the venturi to draw in ozone and dissolve it thoroughly.
Another shortcoming of previous art in the design of small undercounter and countertop ozone systems has been the use of high voltage alternating current transformers, typically producing upwards of 4,000 volts AC. Inasmuch as these transformers must be in close proximity to the ozone generation electrodes, which, in turn, must be in close proximity to the water being treated, hazardous conditions are presented which make such systems unacceptable for household or small commercial applications. Alternating current-based ozone systems also cannot be utilized in remote applications, such as emergency water purification or solar powered water purification, without the addition of expensive power converters.
Previous system designs have attempted to utilize low voltage direct current electronics to overcome the hazards associated with high voltage alternating current. However, the electrical design employed transistorized computer chip technology to deliver spiked direct current to an electrical coil, which, in turn, supplied power to the corona producing electrodes. The shortcomings of this design are that the transistor of the chip heats rapidly, which results in the fading of its ability to produce a consistent level of ozone.